Trouble going up the stairs and standing up sometimes?

My dog (7 yrs old) jumped off my bed yesterday morning and limped immediately after but was walking w/ no limp within a few minutes. I thought she was fine but a few hours later she tried to get up the stairs and couldn't without help. A few times she's also had trouble getting up. It's her back paws but I'm having trouble determining whether it's one or both (but it seems to me like her right back paw). Once she starts up the stairs she seems ok but moves sort of sideways. When she's outside she walks around a little bit and then lays down. She will bark at the bottom of the deck steps to let us know she wants to come in & needs help (not typical of her).
She's overweight (which I take full responsibility for and I am working on getting her to a healthy weight) which makes me think even more that it's an injury (I've also considered muscle weakness as a result of a disorder but it started after jumping off the bed).
I plan on taking her to the vet but any advice in the meantime?